Method for regulating a property of a product derived from a chemical transformation

ABSTRACT

The invention concerns a method for regulating a property of a product derived from a chemical transformation process, consisting in: a) modelling the relationship between said property and characteristic physical quantities of the process; b) fixing a set point value for said property; c) introducing said set point value in a regulation system based on the model obtained in (a) so a to apply to the process at least a physical quantity calculated from said set point value; d) calculating with a model defined in (a), corrected by a factor taking into account the delay, of a model value of the property of the product corresponding to the characteristic physical quantity/quantities defined by the regulation system; e) continuously measuring the real value of the property and the model value of the property of the product; f) determining the difference between said real value and the model value of the property of the product; g) using said difference, after filtering, to adapt the set point value so as to align the real value and its model value. The invention also concerns a regulating device and a chemical transformation method using said device for implementing said method.

[0001] The present invention relates to a method of regulating aproperty of a product resulting from a chemical transformation processand to a regulating device, as well as to a chemical transformationprocess using such a method or such a regulating device.

[0002] The industrial application of any chemical transformationprocess, such as for example a synthesis, polymerization, degradation ordepolymerization process, requires, on the one hand, that relativelystrict technical specifications for the product be met and, on the otherhand, that the incoming material be used economically and efficiently.The inevitable automation that results therefrom therefore requiressuitable, but flexible, control or regulating methods that allow thechemical processes to be optimally controlled.

[0003] The mathematical modeling attempts that are based on thesemethods are as numerous as the chemical processes to be controlled. Themodels conventionally employed are those of the PID type (that is to saythose comprising a proportional term, an integral term and adifferential term) for individually controlling a relatively largenumber of parameters (for example temperature, pressure, flow rates,etc.). However, this type of model is not easily applicable to a largenumber of chemical transformation processes, since these are oftenblemished by lengthy downtimes or delays, either in the process itselfor in the measurements needed for feeding into the model. Theseconsequently result in substantial amounts of scrap that does not complywith the specifications set, for example due to the phenomenon ofoscillation caused by the parameters in the model being corrected toolate and therefore often too much.

[0004] The prediction techniques developed for responding to thelimitations of the conventional methods has not been able successfullyto supplant these methods which are simple to employ.

[0005] It would therefore be desirable to have an entirely automatableregulating method which is simpler and better suited to chemicaltransformation processes.

[0006] The present invention consequently provides a method ofregulating a property of a product resulting from a chemicaltransformation process, consisting:

[0007] a) in modeling the relationship between said property andcharacteristic quantities of the process;

[0008] b) in setting a setpoint value for said property;

[0009] c) in introducing this setpoint value into a regulating systembased on the model obtained in (a) so as to apply at least onecharacteristic quantity, computed from this setpoint value, to theprocess;

[0010] d) in computing, by means of the model defined in (a), correctedby a factor that takes the delay into account, of a model value of theproduct property corresponding to the characteristic quantity/quantitiesdefined by the regulating system;

[0011] e) in continuously measuring the actual value of the productproperty;

[0012] f) in determining the difference between this actual value andthe model value of the product property; and

[0013] g) in using this difference, after filtering, to adapt thesetpoint value so as to align the actual value and its model value.

[0014] According to a preferred variant, the regulating method accordingto the invention includes the computing (d) of the model value of theproperty corresponding to the characteristic quantity/quantities usingthe model obtained in (a), corrected by the factor that takes the delayinto account and by a factor that takes the dynamics of the process intoaccount.

[0015] Such a method, which comprises only a single regulating loop andwhich does not involve direct comparison between the setpoint value andthe actual value of the property, consequently has an advantage in termsof simplicity over the conventional techniques which comprise aregulation based on the comparison of the actual value with the setpointvalue on which is superposed a regulation involving, separately, a modelfor the process and a model for the delay. Moreover, the use of definedmathematical models for computing the model values makes it possible tocomputerize, and consequently completely automate, the process withoutthe need for any human intervention with regard to compensating for theerrors due to the delay or for other external perturbations.

[0016] This method may be employed for any chemical transformationprocess, such as a synthesis process, a polyaddition process, apolymerization process, a grafting process, a degradation process, etc.However, it should be understood that the envisioned process may alsoinclude other treatment steps, whether they be of a chemical natureand/or of a physical nature, which are needed for obtaining the desiredend product. As an example, mention may be made of homogenization,mixing, washing, drying, granulation, molding, etc.

[0017] The relevant product property (or properties) to be monitored andto be regulated obviously depends (or depend) both on the processemployed and on the objective pursued. As a nonexhaustive illustration,mention may be made of the chemical characteristics, such as the natureor the composition of the resulting product, but above all of thephysical characteristics, such as the molecular weight or the molecularweight distribution, the melting point, the stiffness, the viscosity,the melt flow index (MFI), the melt swell, the bubble stability, etc.

[0018] One particular embodiment of the present invention provides forsuch a regulating method to be applied to a process for transforming apolymer in an extruder. For example, this may be a polymer crosslinkingprocess in which crosslinking agents chosen, for example, from peroxidecompounds and diazo compounds are used. It is preferably adepolymerization process using, as reactants, one or more polymers andone or more depolymerization agents.

[0019] The objective of this depolymerization may, for example, be toadjust the Theological properties of the end product, saiddepolymerization very often including other steps (called post-treatmentsteps), for example granulation of the product output by the extruder.

[0020] The polymers envisioned include olefin polymers and copolymerscontaining two to eight carbon atoms, for example ethylene, propylene,etc. Typical polyolefins are ethylene and propylene polymers andcopolymers, such as for example a polypropylene (PP) homopolymer andcopolymers of propylene with secondary amounts of other olefins.

[0021] The nature of the depolymerization agents is not criticalprovided that they are suitable for this purpose. Examples are oxygen,oxygen-rich compounds, such as peroxides, persulfates and diazocompounds. Preferred depolymerization agents include diaryl, dialkyl andarylalkyl peroxides. 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane is verysuitable. It is also possible to use several depolymerization agentsseparately or as a mixture.

[0022] The “reactants”, as used within the context of the presentinvention, also includes other substances which are necessary for theenvisioned process to be carried out correctly, but which are notdirectly involved in the reaction or reactions proper. These may be anyuseful additives or adjuvants, such as stabilizers, antioxidants,antistatic agents, organic dyes, mineral pigments and fillers, etc., itbeing possible for these additives and adjuvants to be added at anyappropriate moment. Thus, the addition may take place simultaneously, inmixing, successively or even at different steps of the process,depending on the nature and the function of the additive or adjuvant inquestion.

[0023] Another aspect of the present invention envisions measuring theactual value of the product property on a specimen of the end productand not on an intermediate product, as the prior art dictates, in orderto reduce the effect of the delay. This is because, as we mentionedabove, the great majority of chemical transformation processes used inindustry involve several chemical and/or physical steps before theintended product is obtained. The properties of this product areconsequently liable to change over the duration of the process.

[0024] This variant of the present invention thus has the furtheradvantage of also integrating, into the regulation, other perturbationsthat are associated with the post-treatment of the product.

[0025] The technical instrumentation used to analyze the product and todetermine the actual value of the product property obviously depends onthe latter, but is not critical. The choice will furthermore depend onthe simplicity of implementation, the reliability, the rapidity or theavailability. For example, for determining the melt flow index (MFI),rheometric techniques, spectroscopic methods (IR, NIR, NMR) andultrasonic analyses are suitable, but not exclusive.

[0026] The actual value of the property is used to determine thedifference between this actual value and the model value, that is to saythe value computed by means of the mathematical model and corrected bythe delay factor and optionally the dynamic factor. This difference isthen employed to adapt the setpoint value so as to align the actualvalue and the model value. In a preferred aspect of the presentinvention, this difference is, however, firstly subjected to a filteringstep for the purpose of moderating the aggressiveness of the regulator,for example by introducing an appropriate filter, such as a filter ofthe low-pass type with an adjustable time constant, in the control loop.

[0027] The mathematical model involved in the method of the presentinvention may be based on an equation of the type: $\begin{matrix}{{MV} = {a + {bIV} + {\sum\limits_{i = 1}^{n}{\sum\limits_{j = 1}^{p}{c_{ij}\left\lbrack R_{j} \right\rbrack}^{i}}} + {\sum\limits_{i = 1}^{n}{\sum\limits_{j = 1}^{p}{d_{ij}\lbrack{Tj}\rbrack}^{i}}} +}} \\{{{\sum\limits_{i = 1}^{n}{\sum\limits_{j = 1}^{p}{e_{ij}\left\lbrack P_{j} \right\rbrack}^{i}}} + {\sum\limits_{i = 1}^{n}{\sum\limits_{j = 1}^{p}{f_{ij}\lbrack{Fj}\rbrack}^{i}}}}}\end{matrix}$

[0028] where:

[0029] MV represents the model value or estimated value;

[0030] IV represents the initial value of the property;

[0031] [R_(j)] represents the concentrations of the reactants;

[0032] [T_(j)] represents characteristic temperatures of the process;

[0033] [P_(j)] represents characteristic pressures of the process;

[0034] [F_(j)] represents the flow rates of the reactants;

[0035] a, b, c_(ij), d_(ij), e_(ij) and f_(ij) are constants;

[0036] i and j are natural integers greater than or equal to 1.

[0037] Another embodiment of the present invention is a regulatingmethod in which the model is based on an equation of the type:$\begin{matrix}{{\log \quad {MV}} = {a^{\prime} + {b^{\prime}\quad \log \quad {IV}} + {\sum\limits_{i = 1}^{n}{\sum\limits_{j = 1}^{p}{c_{ij}^{\prime}\left\lbrack R_{j} \right\rbrack}^{i}}} + {\sum\limits_{i = 1}^{n}{\sum\limits_{j = 1}^{p}{d_{ij}^{\prime}\lbrack{Tj}\rbrack}^{i}}} +}} \\{{{\sum\limits_{i = 1}^{n}{\sum\limits_{j = 1}^{p}{e_{ij}^{\prime}\left\lbrack P_{j} \right\rbrack}^{i}}} + {\sum\limits_{i = 1}^{n}{\sum\limits_{j = 1}^{p}{f_{ij}^{\prime}\lbrack{Fj}\rbrack}^{i}}}}}\end{matrix}$

[0038] where:

[0039] MV, IV, [R_(j)], [T_(j)], [P_(j)], [F_(j)], i and j have themeanings indicated above and a′, b′, c′_(ij), d′_(ij), e′_(ij) andf′_(ij) are constants.

[0040] The factor taking the delay into account may be represented byany suitable known method, for example the method of the “Smithpredictor” as described, for example, in Chemical Engineering Progress,Vol. 53, No. 5, May 1957, pages 217-219. An advantageous embodiment forimplementing the regulating method according to the invention providesfor the factor taking the delay into account to be obtained by using ashift register. The factor taking the dynamics of the process intoaccount is advantageously represented by an “LAG”-type function or alow-pass filter. One function of this particularly simple type givinggood results is a function following the formalism of Laplace transformssatisfying the equation y(t)=1/(1+pTp) in which p represents the periodof the measurement and Tp the time constant of the process. Such methodsand functions are well known to those skilled in the art.

[0041] Furthermore, the present invention provides, according to anotheraspect, a device for regulating a property of a product resulting from achemical transformation process, comprising:

[0042] at least one unit for regulating at least one characteristicquantity on the basis of a setpoint value of the property to beregulated;

[0043] at least one computing unit for determining a model value of theproperty to be regulated on the basis of the values of thecharacteristic quantity/quantities defined by the regulator;

[0044] means for continuously measuring the actual value of the productproperty;

[0045] means for determining the difference between the actual value andthe model value of the property and for filtering this difference; and

[0046] means for adapting the setpoint value so as to reduce thisdifference,

[0047] The device according to the invention preferably uses aregulating method in accordance with the present invention in the mannerdescribed above.

[0048] Another embodiment provides a device in which the computing unituses a model with proportional, integral and/or differential terms,corrected by a factor taking the delay into account and possibly by afactor taking the dynamics of the process into account.

[0049] In one embodiment, the regulating unit uses the inverse of themodel generated for the computing unit.

[0050] The characteristic quantities of the chemical transformationprocess that can be controlled by the device of the invention arechosen, for example, from among the concentrations and flow rates of thereactants, the residence times, the pressures and/or temperatures of oneor more of the steps of the process.

[0051] Moreover, the present invention envisions a chemicaltransformation process that uses a regulating device as described above,or employing a regulating method according to the invention, formonitoring and regulating a property of a product resulting from achemical transformation process.

[0052] As indicated above, this chemical transformation may represent orcomprise, for example, one or more synthesis, polyaddition,polymerization, grafting and/or degradation steps and, optionally, oneor more physical procedures, such as homogenization, mixing, drying,granulation, molding, etc. The preferred process according to theinvention is a depolymerization reaction using one or more polymers andone or more depolymerization agents as reactants.

[0053] The nature of the polymers was described above and is preferablya polyolefin, such as polypropylene.

[0054] The depolymerization agent/s is/are chosen especially from amongoxygen, oxygen-rich compounds, peroxides, persulfates and diazocompounds, as described above.

[0055] As we have mentioned above, it is in principle possible tomonitor any property of the end product. Thus, in one method ofimplementing the process according to the present invention, the productproperty to be monitored and regulated is the melt flow index (MFI) byacting on the abovementioned parameters. The melt flow index isdetermined, for example, continuously using a rheometer, an IRspectrometer, an NIR spectrometer, an NMR spectrometer and/or anultrasonic analyzer, either directly in line or preferably on a specimenof the end product.

[0056] The in-line measurement involves the withdrawal of part of theproduct stream, for example in the case of an extrusion upstream of thedye in order to feed the chosen analyzer, for example a rheometer.However, apart from the drawback that such a measurement does notconsider any variations associated with the post-treatment of theproduct, further disadvantages must be taken into consideration,especially a delay that is nevertheless long (compared with the timeconstant of the process), even in the case of in-line measurement, theproximity of sensitive measurement apparatuses and/or the resultingspace requirement of the production plant.

[0057] Continuous determination on the end product is thereforepreferred. It should be noted that what is meant by continuousmeasurement of the actual value of the product property is a measurementcarried out at a regular rate by means of an automatic apparatus.

[0058] When the process according to the present invention is applied tothe regulation of the MFI, the model value of the MFI may be computed onthe basis of the model:

MFI _(OUT) =A+B. MFI _(IN) +c.[PER]+D.T

[0059] where:

[0060] MFI_(out) represents the estimated melt flow index of thedepolymerization product;

[0061] MFI_(in) represents the melt flow index of the polymer reactant;

[0062] A, B, C and D represent constants;

[0063] [PER] represents the concentration of depolymerization agent inthe material entering the process; and

[0064] T represents the temperature at which the depolymerizationreaction takes place.

[0065] In other cases, the process applied to the regulation of the meltflow index (MFI) of a polymer, in which the model of the MFI satisfies afirst-order equation in the concentration of depolymerization agent([PER]) of the type:

logMFI _(out) =A′+B′.logMFI _(in) +C′.[PER]+D.T

[0066] or else a second-order equation

logMFI _(0out) =A″+B″.logMFI _(in) +C ₁ ″.[PER]+C ₂ ″.[PER] ² +D″.T

[0067] where

[0068] MFI_(out), MFI_(in), [PER] and T have the meanings given aboveand A′, B′, C′, D′, A″, B″, C₁″, C₂″ and D″ represent constants.

[0069] The delay factor and the dynamic factor are those described abovewithin the context of the present invention and may be defined by anymethods known per se, such as more particularly those mentioned above.

[0070] In practice, although the models adopted above implicitly use theconcentration of the depolymerization agent to regulate the melt flowindex, it is also possible to acquire this property more simply byadjusting the feed flow rate of the depolymerization agent. In thelatter case, it is assumed that volume variation due to variable amountsof depolymerization agent or, in other words, the dilution effect, isnegligible.

[0071] In one practical method of implementation, the flow rate(concentration) of the depolymerization agent(s) is in turn regulated bya simple local feedback loop, for example of the PID type, so as tocontrol the flow rate (the concentration) actually delivered by themetering devices.

[0072] The actual flow rate may be determined by any device suitable forthis purpose, generally a flow meter, such as a Coriolis flow meter.Another very simple and often sufficient possibility is to infer theflow rate from the speed of rotation and from the stroke of the pistonof the pump.

[0073] The model on the basis of the method of the present invention mayin some cases be further simplified. Unless raw materials ofsufficiently constant quality are used, it may be assumed, for example,that the polymer reactant melt flow index (MFI_(in)) is invariable.

[0074] The same applies to the temperature (T): if the process iscarried out under essentially steady-state conditions, the equation isfurther simplified.

[0075] In practice, the model will then be reduced to a first-orderlinear model in a single variable. The factor that takes the delay intoaccount may also be reduced to a pure delay and may be employed by anysuitable method, for example by the “Smith predictor” approach or byusing a shift register. In practice too, the factor taking the dynamicsof the process into account is usually reduced to a first-order low-passfilter.

[0076]FIG. 1 shows the overall method according to the invention.

[0077]FIG. 2 shows the diagram of one possible application of thepresent invention, namely a depolymerization process that is regulatedby a method of the present invention.

[0078]FIG. 3 shows the case of FIG. 2 using a simplified first-ordermodel, assuming that the temperature and the melt flow index (MFI) areconstant.

[0079]FIG. 4 shows examples of the performance obtained in the case of aPP resin.

[0080] As FIG. 1 shows, the setpoint value (SP) is introduced into theregulating system (regulator 1) based on the model generated in step (a)and using, for example, the inverse of this model.

[0081] The result of the regulation acts on the process (2) byregulating the actual value of the property (PV) and on the model (3) inorder to compute the model value (MV). The actual value (PV) is measuredand compared with the model value (MV) in order to determine thedifference (E) therebetween. This difference is then filtered and thefiltered difference (Ef) is used to adapt the setpoint (SP).

[0082]FIG. 2 is an example of how the present method is applied. Thefirst case concerns a process used for adjusting the rheologicalcharacteristics of polypropylene (PP) resins. The initial resin (fluffA) and other additives (B) are mixed in the extruder (1) then adepolymerization agent (L) is added, before the compound is extruded andgranulated. The typical duration of this first step is around 0.1minutes. The granules are then washed (2), drained (3) and dried (4).This step typically takes 0.5 minutes. The resulting granules thatrepresent the end product are then subjected to rheological measurements(MFI) after melting them, for example in a Göttfert-type rheometer. Thetime taken in this case is, for example, around 5 to 20 minutes.

[0083] If the diagram in FIG. 1 is applied to the process of FIG. 2, thediagram in FIG. 3 is obtained. In the case of said FIG. 3, the model isa simplified model of the type MFI_(out)=K+g.[PER] (as describedabove)—the factor taking the dynamics into account is a function of thetype $\frac{1}{1 + {p \cdot {TP}}},$

[0084] using the formalism of Laplace transforms, and also describedabove.

[0085] τ is the delay and the filter is produced by a function of thetype $\frac{1}{1 + {p \cdot {Tp}}}$

[0086] (using the Laplace formalism) in which p represents the period ofthe measurement and Tf the response time of the filter.

[0087] As we saw in FIG. 2, the typical delay (τ) ranges from 5 to 20minutes or longer. The factor taking the delay into account is in thiscase, for example, a Smith predictor or any other appropriate method.The setpoint (MFI_(SP)) is used to determine the amount (orconcentration) [PER]_(SP) of depolymerization agent needed. Thisconcentration is then introduced into the model and the result, that isto say the model value, is compared with the actual value (MFI_(PV)) inorder to determine the difference (E) between them. After filtering, thefiltered difference (E_(f)) is used to adapt the setpoint (MFI_(SP)).

[0088] The concentration of depolymerization agent is varied by anamount Δ[PER]. After a delay τ, the MFI_(out) in turn starts to varyuntil it again stabilizes at a value MFI_(out)+ΔMFI_(out). The variousregulating parameters may then be determined as follows:${process}\quad {gain}\begin{matrix}: & {{g = \frac{\Delta \quad {MFI}_{out}}{\Delta \lbrack{PER}\rbrack}};}\end{matrix}$

[0089] constant of the model K=MFI_(out)−g.[PER];

[0090] the time constant of the process: Tp=time needed to reach 63% ofthe ΔMFI_(out) taking the delay τ into account;

[0091] the time constant relating to filtering the difference E betweenthe measured value and the computed value is set to 1.5 min.

[0092] The following example and FIG. 4 illustrate the invention.

EXAMPLE

[0093] A polypropylene (PP) resin with an initial MFI of around 1 g/10min undergoes depolymerization. The depolymerization is carried out onceusing a conventional PID-type regulating method and once using theregulating method of the present invention based on a first-ordermodel+delay+dynamic factor.

[0094]FIG. 4 illustrates the performance obtained with and withoutregulation according to the present invention (graphs 4A and 4B,respectively). In the graphs, the time expressed in hours is plotted onthe x-axis and the MFI expressed in g/10 min, measured using a Göttfertapparatus, is plotted on the y-axis. The graphs also indicate the upperand lower limits of the specifications.

1. A method of regulating a property of a product resulting from achemical transformation process, consisting: a) in modeling therelationship between said property and characteristic quantities of theprocess; b) in setting a setpoint value for said property; c) inintroducing this setpoint value into a regulating system based on themodel obtained in (a) so as to apply at least one characteristicquantity, computed from this setpoint value, to the process; d) incomputing, by means of the model defined in (a), corrected by a factorthat takes the delay into account, of a model value of the productproperty corresponding to the quantity/characteristic quantities definedby the regulating system; e) in continuously measuring the actual valueof the product property; f) in determining the difference between thisactual value and the model value of the product property; and g) inusing this difference, after filtering, to adapt the setpoint value soas to align the actual value and its model value.
 2. The regulatingmethod as claimed in claim 1, in which the model value corresponding tothe characteristic quantity/quantities is computed using the modeldefined in (a) corrected by the factor that takes the delay into accountand by a factor that takes the dynamics of the process into account. 3.The regulating method as claimed in either of claims 1 and 2, applied toa process for transforming a polymer in an extruder such as, forexample, a depolymerization process using one or more polymers and oneor more depolymerization agents as reactants.
 4. The method as claimedin any one of claims 1 to 3, in which the actual value of the productproperty is measured on a specimen of the end product.
 5. The regulatingmethod as claimed in any one of the preceding claims, in which thefilter used is a low-pass-type filter.
 6. The regulating method asclaimed in any one of claims 1 to 5, in which the model is based on anequation of the type: $\begin{matrix}{{MV} = {a + {bIV} + {\sum\limits_{i = 1}^{n}{\sum\limits_{j = 1}^{p}{c_{ij}\left\lbrack R_{j} \right\rbrack}^{i}}} + {\sum\limits_{i = 1}^{n}{\sum\limits_{j = 1}^{p}{d_{ij}\lbrack{Tj}\rbrack}^{i}}} +}} \\{{{\sum\limits_{i = 1}^{n}{\sum\limits_{j = 1}^{p}{e_{ij}\left\lbrack P_{j} \right\rbrack}^{i}}} + {\sum\limits_{i = 1}^{n}{\sum\limits_{j = 1}^{p}{f_{ij}\lbrack{Fj}\rbrack}^{i}}}}}\end{matrix}$

where: MV represents the model value or estimated value; IV representsthe initial value of the property; [R_(j)] represents the concentrationsof the reactants; [T_(j)] represents characteristic temperatures of theprocess; [P_(j)] represents characteristic pressures of the process;[F_(j)] represents the flow rates of the reactants; a, b, c_(ij),d_(ij), e_(ij) and f_(ij) are constants; i and j are natural integersgreater than or equal to
 1. 7. The regulating method as claimed in anyone of claims 1 to 5, in which the model is based on an equation of thetype: $\begin{matrix}{{\log \quad {MV}} = {a^{\prime} + {b^{\prime}\quad \log \quad {IV}} + {\sum\limits_{i = 1}^{n}{\sum\limits_{j = 1}^{p}{c_{ij}^{\prime}\left\lbrack R_{j} \right\rbrack}^{i}}} + {\sum\limits_{i = 1}^{n}{\sum\limits_{j = 1}^{p}{d_{ij}^{\prime}\lbrack{Tj}\rbrack}^{i}}} +}} \\{{{\sum\limits_{i = 1}^{n}{\sum\limits_{j = 1}^{p}{e_{ij}^{\prime}\left\lbrack P_{j} \right\rbrack}^{i}}} + {\sum\limits_{i = 1}^{n}{\sum\limits_{j = 1}^{p}{f_{ij}^{\prime}\lbrack{Fj}\rbrack}^{i}}}}}\end{matrix}$

where: MV represents the model value or estimated value; IV representsthe initial value of the property; [R_(j)] represents the concentrationsof the reactants; [T_(j)] represents characteristic temperatures of theprocess; [P_(j)] represents characteristic pressures of the process;[F_(j)] represents the flow rates of the reactants; a′, b′, c′_(ij),d′_(ij), e′_(ij) and f′_(ij) are constants; i and j are natural integersgreater than or equal to
 1. 8. The regulating method as claimed in anyone of claims 1 to 7, in which the factor taking the delay into accountis obtained using a shift register.
 9. The regulating method as claimedin any one of claims 1 to 8, in which the factor taking the dynamics ofthe process into account is represented by an LAG-type function or alow-pass filter.
 10. A device for regulating a property of a productresulting from a chemical transformation process, comprising: at leastone unit for regulating at least one characteristic quantity on thebasis of a setpoint value of the property to be regulated; at least onecomputing unit for determining a model value of the property to beregulated on the basis of the values of the characteristicquantity/quantities defined by the regulator; means for continuouslymeasuring the actual value of the product property; means fordetermining the difference between the actual value and the model valueof the property and for filtering this difference; and means foradapting the setpoint value so as to reduce this difference.
 11. Thedevice as claimed in claim 10, characterized in that it uses a method asclaimed in any one of claims 1 to
 9. 12. The device as claimed in claim10, in which the computing unit uses a model with proportional, integraland/or differential terms, corrected by a factor taking the delay intoaccount and possibly by a factor taking the dynamics of the process intoaccount.
 13. The device as claimed in claim 12, in which the regulatoruses the inverse of the model generated for the computing unit.
 14. Thedevice as claimed in any one of claims 10 to 13, in which thecharacteristic quantities of the chemical transformation process arechosen from among the concentrations and flow rates of the reactants,the residence times, the pressures and/or temperatures of one or more ofthe steps of the process.
 15. A chemical transformation process using aregulating device according to any one of claims 10 to 14 or employing aregulating method as claimed in any one of claims 1 to 9 for monitoringand regulating a property of a product resulting from a chemicaltransformation process.
 16. The process as claimed in claim 15,characterized in that the chemical transformation is a depolymerizationreaction using one or more polymers and one or more depolymerizationagents as reactants.
 17. The process as claimed in claim 16,characterized in that at least one of the polymers is a polyolefin. 18.The process as claimed in claim 17, characterized in that the polyolefinis polypropylene.
 19. The process as claimed in any one of claims 16 to18, characterized in that at least one depolymerization agent is chosenfrom among oxygen, oxygen-rich compounds, peroxides, persulfates anddiazo compounds.
 20. The process as claimed in any one of claims 16 to19, characterized in that the product property to be monitored andregulated is the melt flow index (MFI).
 21. The process as claimed inclaim 20, characterized in that the melt flow index (MFI) is determinedusing a rheometer, an IR spectrometer, an NIR spectrometer, an NMRspectrometer and/or an ultrasonic analyzer.
 22. The process as claimedin any one of claims 15 to 21, characterized in that the actual value ofthe product property is determined directly in line.
 23. The process asclaimed in claim 22, characterized in that the actual value of theproduct property is determined on a specimen of the end product.
 24. Theprocess as claimed in any one of claims 16 to 23, applied to theregulation of the melt flow index (MFI) of a polymer, in which the modelvalue of the MFI may be computed on the basis of the model: MKI _(out)=A+B.MFI _(in) +C.[per]+D.T where: MFI_(out) represents the estimatedmelt flow index of the depolymerization product; MFI_(in) represents themelt flow index of the polymer reactant; A, B, C and D representconstants; [PER] represents the concentration of depolymerization agent;and T represents the temperature at which the depolymerization reactiontakes place.
 25. The process as claimed in any one of claims 16 to 23,applied to the regulation of the melt flow index (MFI) of a polymer, inwhich the model value of the MFI is computed on the basis of the model:logMFI _(out) =A′+B′.logMFI _(in) +C′.[PER]+D′T where: MFI_(out)represents the estimated melt flow index of the depolymerizationproduct; MFI_(in) represents the melt flow index of the polymerreactant; A′, B′, C′ and D′ represent constants; [PER] represents theconcentration of depolymerization agent; and T represents thetemperature at which the depolymerization reaction takes place.
 26. Theprocess as claimed in any one of claims 16 to 23, applied to theregulation of the melt flow index (MFI) of a polymer, in which the modelvalue of the MFI is computed on the basis of the model: logMFI _(OUT)=A″+B″.logMFI _(in) +C ₁ ″.[PER] ² D″.T where: MFI_(out) represents theestimated melt flow index of the depolymerization product; MFI_(in)represents the melt flow index of the polymer reactant; A″, B″, C₁″ C₂and D″ represent constants; [PER] represents the concentration ofdepolymerization agent; and T represents the temperature at which thedepolymerization reaction takes place.
 27. The process as claimed in anyone of claims 24 to 26, in which the delay factor is obtained using ashift register.
 28. The process as claimed in any one of claims 24 to26, in which the factor taking the dynamics of the process into accountis represented by a first-order low-pass filter.
 29. The process asclaimed in any one of claims 24 to 28, in which the melt flow index isregulated by adjusting the concentration of depolymerization agent or byadjusting the flow rate of said depolymerization agent.
 30. The processas claimed in any one of claims 24 to 29, characterized in that the meltflow index of the polymer reactant (MFI_(in)) and/or the temperature (T)are assumed to be constant.